Transport Block Processing using LDPC Coding

Data delivered from the MAC layer to the physical layer is termed as a transport block. For the downlink shared channel (DL-SCH), a transport block goes through the processing stages of:

CRC attachment,

Code block segmentation and code block CRC attachment,

Channel coding using LDPC,

Rate matching and code block concatenation

before being passed on to the physical downlink shared channel (PDSCH) for scrambling, modulation, layer mapping and resource/antenna mapping. Each of these stages is performed by a function as shown next.

The output number of bits from the rate matching and code block concatenation process must match the bit capacity of the PDSCH, based on the available resources. In this example, as the PDSCH is not modeled, one can select either of puncturing or repetition or full coded block transmission using the punctLen, and repLen parameters to specify the respective lengths.

Channel

A simple bipolar channel with no noise is used for this example. With the full PDSCH processing, one can consider fading channels, AWGN and other RF impairments as well.

chOut = double(1-2*(chIn));

Receive Processing using LDPC Decoding

The receive end processing for the DL-SCH channel comprises of the corresponding dual operations to the transmit end that include

As the displays indicate, there are no CRC errors at both the code-block and transport block levels. This leads to the transport block being recovered and decoded with no errors, as expected, for a noiseless channel.